Petts Wood does carry a flood risk, but the water to worry about falls from the sky. Almost none of the area is in a river or sea flood zone. Even so, about one postcode in five rates high on at least one flood measure, and another one in five rates medium. Petts Wood's river risk is small. Its drains are the bigger concern.
The Environment Agency's river-and-sea flood zones cover about 1% of the area's postcodes in zone 2 and less than 1% in zone 3. The two are separate bands. Zone 3 is the highest-probability land, and zone 2 is the medium-probability fringe beyond it, so a smaller zone 3 share means less high-risk land. The Environment Agency's records list 17 past flood events in the area. The most recent was in August 1977, when a main river overflowed its channel with no raised defences in the way.
Surface water is a different problem, and the river zones don't measure it. It comes from heavy rain that the ground and the drains can't take fast enough. It collects in dips, underpasses and the low end of a road, sometimes miles from any river. A house can be well outside every river flood zone and still have water at the back door after a summer storm.
The Environment Agency also has a climate-adjusted flood zone, which assumes wetter conditions to come, and it covers about 6% of the area's postcodes. That is a modelled look at future river and sea risk, and it's noticeably bigger than the zones in force today.
Insurers price surface-water risk along with river risk. A home on a flagged postcode can face higher premiums, a bigger excess or more questions at renewal, even with no river nearby. Ask the seller, through their solicitor, whether the property has ever made a flood or drainage claim. Ask early, because the answer can change what you are prepared to pay.
The broadest view combines every measure. About 19% of the area's postcodes rate high, 20% medium and 40% low on at least one flood indicator. Any of several measures can flag a postcode, surface water included, and that's why these shares are so much larger than the river-zone figures. Two neighbouring streets can rate differently because one of them is a few feet lower.
The Environment Agency's rivers-and-sea mapping also counts individual properties. Across the 31 postcodes in the area that carry any river or sea risk, 737 properties are listed. Of those, 61 are rated high risk, 54 medium, 81 low and 8 very low, and 57 of the high-risk properties are homes. Postcodes with no river or sea risk don't appear in this count at all.
About 0.4% of postcodes fall inside the high-probability flood extent whether or not defences are included in the model. In other words, any defences here make no visible difference to the modelled high-risk area. "Defended" in these maps only means that a defence exists in the model. It is no promise about what happens to a particular house in a particular storm.
The nearest tide gauge is at Dover, which recorded sea levels rising by about 2 millimetres a year between 1961 and 2010. That is a measured rate for one place on the coast. Petts Wood is a long way inland, and the sea is the least of its flood problems.
Flood risk is the weakest thing about Petts Wood, and it comes almost entirely from surface water. The river maps make the place look safer than it is, so any buyer should check the surface-water risk for the exact postcode.